media: mtk-vcodec: Remove VA from encoder frame buffers

The encoder driver has no need to do any CPU access to the source frame
buffers. Use a separate structure for holding DMA addresses and sizes
for those and remove, so we do not end up introducing any erroneous
dereferences of those VAs.

This fixes DMA-buf import from exporters that do not provide contiguous
kernel mappings, which includes the MTK DRM driver.

Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>